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Determination Of Thickness And Optical Constants Of Metal Films And Research Of Oscillating-Field Sensors Based On Symmetrical Metal-Clad Waveguide

Posted on:2009-02-26Degree:DoctorType:Dissertation
Country:ChinaCandidate:J H GuFull Text:PDF
GTID:1118360302966582Subject:Optics
Abstract/Summary:PDF Full Text Request
With the development of modern science and technology, especially the development of emerging science such as life sciences and clinical medicine, the biological survey and the sensing face growing challenge, the need for more sensitive biosensor has increased rapidly as well. After studying the conventional biosensors based on evanescent-field sensing, a symmetrical metal-clad waveguide (SMCW) sensor based on oscillating-field sensing is proposed.Different from the common dielectric waveguide, the cladding layer of SMCW is constructed by two thin metal films. Measurement of thickness and optical constants of thin metal films is also a research subject of our article. An extended attenuated total reflection (ATR) spectrum, which consists of a surface plasmon resonance (SPR) dip and a total internal reflection (TIR) step, is used to determine the optical constant and the thickness of a thin metal film at a given frequency in the conventional Kretschmann configuration. Previous research has shown that two sets of solutions for the optical constant and thickness can be obtained from a SPR dip, and the ambiguity should be removed by carrying out another angular scan process or employing a more complicated structure. However, we find that the true solution can be simply selected by a new parameter that denotes the TIR step change. Our method can avoid not only the troubles caused by the double-scan techniques, but also the increased difficulties due to the existence of an additional polymer film in a single-scan method.Due to the special optical properties of the metal film, the characteristic of SMCW is greatly different from the common dielectric waveguide in many aspects, such as the waveguide layer can be enlarged to millimeter scale, the ultra-high order modes in SMCW is very sensitive to refractive change of the waveguide, and present polarization independence. These unique features enable us to fabricate an oscillating-filed sensor based on SMCW. The samples are introduced into the waveguide layer and probed by the ultra-high order modes. Owing to the concentrated power in the sensing region and the use of very sensitive ultra-high order modes, the SMCW sensor gains a sensitivity enhancement of 1 to 2 orders of magnitude than that of the previous sensor structure.To verify the performance of the proposed SMCW sensor, several experiments with different measurement interrogation are carried out. Using the NaCl water solutions as samples, we obtain a sensitivity of 424o/RIU and resolution of 7.3×10-6RIU by applying an angular interrogation, and a resolution of 0.88×10-6RIU by applying an intensity interrogation. When employed as an absorption sensor, with the methylene blue solutions as samples, the SMCW structure achieves a resolution of 5×10-6, and avoides the surface adsorption effect of methylene blue solutions.It is demonstrated both theoretically and experimentally that the SMCW senor based on oscillating-filed sensing is more sensitive and easy fabricated, and has the potential applications in high sensitivity, low cost and accurate bio-sensing science.
Keywords/Search Tags:Metal film, Optical constants, ATR, SPR, Waveguide, biosensor, Symmetrical metal-clad waveguide, Sensitivity, Resolution, Refractive index, Absorption coefficient
PDF Full Text Request
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